At approximately half the normal life span of a number of mammals, including man, we have demonstrated an altered histochemistry of the media of the arteriolar wall; we have termed these "old" arterioles. However, in old animals with revascularized tissue due to injury, the newly formed arterioles are "young" but age subsequently. The aims of this proposal are: (1) to define and quantitate the chemical (histochemical) and morphological changes in the smallest arteries and arterioles which occur simultaneously in aging; (2) to determine the time course (weeks/months) of the conversion of "young' arterioles to "old" arterioles in the revascularized tissue of injury of old animals "accelerated aging"; (3) to evaluate the relative roles of local environmental (tissue fluid) factors and/or genetic factors in the development of microvascular aging in such revascularized tissues; and (4) to quantify similarly the basal lamina thickening of capillaries and altered adjacent interstitium which are part of the microvascular aging complex. Tissues from various organs will be analyzed to obtain the necessary data from the various ages spanning the natural lifetime of the inbred albino rat. Studies of the revascularized (injured by incision) skin tissue will be in both the (old) donor and (young) recipient animal and the converse. The methods to be used are morphologic and physiologic: the former include histological, histochemical and electron microscopical, and employ quantitative analytic methods to obtain the various data by image scopical, and employ quantitative analytic methods to obtain the various data by image analysis techniques; the latter include microhemodynamics, capillary permeability and vasoactive responses. From these studies it is anticipated that this knowledge of the aging of the microvasculature may lead to further understanding of the alterations in blood flow, diffusion and exchange which may occur in aging. These studies should also provide a precisely defined control model for future research in microvascular aging.